1. Field of the Invention
The invention relates to a process to purge polymer or plastic melt guiding parts of film extrusion systems with at least one extruder for the purpose of changing batches, control and operating units and film extrusion systems to carry out the process.
2. Description of the Related Art
Film extrusion systems to produce films are known. To produce multilayered films, which are called film composites in the following, film extrusion systems with several extruders are installed.
They are categorized, above all, into film bubble extrusion systems and flat film extrusion systems.
Film bubble extrusion systems are equipped with socalled blown film dies, which eject the film bubbles.
In the case of flat film extrusion systems, which produce film with several layers, a so-called feedblock usually assumes, first of all, the uniting of the different polymer or plastic materials. Then, the resulting plastic composite is extruded by a die and a flat film is produced.
Both types of systems are described in detail with reference to embodiments used for the purpose of examples in the description of the object.
In recent years the need for many different types of films and film composites has increased. Therefore, different film composites are frequently produced one after the other by the same film extrusion system. When changing over from one film composite to the next, it is often necessary to clean the parts of the film extrusion system that guide the polymer or plastic material.
This cleaning can be done by dissecting and cleaning the polymer or plastic guiding parts in large volume cleaning units.
However, owing to the enormous expense associated with such a cleaning process, so-called purging phases are often inserted when changing over from one film composite to the next.
During such a purging phase the plastic residues in a film extrusion system are usually purged with other plastic melts.
In so doing, the material of the following film composite is often used. However, it is also possible to use other material that is economical or has good purging properties.
Such a purging process to change over from one film composite to the next film composite can take a long time, since residual material that can be detached only slowly remains sticking in the film extrusion system.
The present invention proceeds from this point.